1. Field of the Invention
The present invention relates to a cation-polymerizable coating composition capable of forming a coating film having excellent surface lubricity and its durability.
2. Description of the Prior Art
As a cation-polymerizable paint used to form a coating film for metal cans or metal cans coated with plastic film, paints containing an epoxy resin and a cation-polymerization initiator are known until now.
The curing of the coating film on the abovementioned metal cans or metal cans coated with plastic film after coating is conducted by baking for a short time or ultraviolet irradiation, on a high speed production line. Metal cans are transported to the next procedures such as inner surface coating step or processing step after the coating and curing. As the coating film is prone to be damaged during the transport, a silicon compound is usually mixed in the paint in order to give lubricity to the surface of the coating film. However, when a silicon compound is mixed in the paint, there tends to occur problems such as cissing at the coating film, whitening of the coating or deteriorated smoothness of the coating film.
In Japanese Laid-open Publication No.291132/1997 there is disclosed an ultraviolet-curing resin composition for metal can containing an epoxy compound, a modified dimethylpolysiloxane having as a side chain a polyoxyalkylene chain containing a hydroxyl group(s), a methoxy group (s) or a methylcarbonyloxy group(s) at the end, and a photocation-polymerization initiator. This publication describes that a coating film with excellent adhesivity, lubricity, retort resistance, coating film hardness, processibility, surface smoothness and transparency can be obtained by coating the composition on a metal can or a deep-drawn metal can coated with polyester film. However, a coating film obtained with the composition has a problem that the lubricity of the coating film after retort treatment is not sufficient.
The main purpose of the present invention is to provide a short time curing type cation-polymerizable coating composition capable of forming a coating film with excellent adhesivity to substrate, lubricity, retort resistance, coating film hardness, processibility, surface smoothness and transparency and, in addition, with excellent lubricity of the coating film after retort treatment.
Another purpose of the present invention is to provide a method of coating metal cans or metal cans coated with plastic film by using the above-mentioned coating composition.
A further purpose of the present invention is to provide an article such as a metal can or a metal can coated with plastic film, coated by using the above-mentioned coating composition.
Other purposes and features of the present invention will be clarified in the following description.